Session: 01-12 Propellers and Open Rotors

Paper Number: 123904

123904 - Design and Analysis of a Liftfan for eVTOL Aircraft 

Ducted liftfans can increase the hovering efficiency of eVTOL aircraft but are not as common as open propellers. Their increased complexity poses three challenges which are addressed in this paper, with the ultimate goal of reducing overall fan length and mass without suffering increased losses due to separations from stronger adverse pressure gradients. 

 

First, instead of the single row of a propeller, the liftfan consists of a complete stage which must be designed as a whole. The preliminary and 3D design variables of the rotor row and splittered diffuser stator row are optimised together using 3D CFD to maximise the hovering figure of merit, a non-dimensional measure of power consumption. The resulting design is then validated by experimental tests of a prototype liftfan.

 

Second, unlike an open propeller, the liftfan is enclosed by a complete nacelle. To be viable it must simultaneously perform effectively during forward flight of the aircraft, as well as in pure hover. A low-order model is developed to investigate the maximum cruise range for different fan designs with varying area ratio (𝜎) and cruise pitch angles (𝛼). The resulting design is validated using full annulus 3D CFD and experimental wind tunnel tests.

 

Third, as the electric motor in a liftfan is mounted inside the hub, fan-driven active cooling is necessary to prevent overheating. The stagnation pressure losses incurred by cooling airflow must be minimised without impeding heat transfer. Low-order models are developed to predict motor heat transfer and loss and to guide the design of a mixed flow cooling fan. The addition of forward sweep and adoption of a high blade count are found to significantly reduce cooling fan loss. This is confirmed with 3D CFD calculations of the cooling fan and experimental test of the prototype.

Presenting Author: Rory Hine University of Cambridge

Presenting Author Biography: PhD Candidate at the University of Cambridge Whittle Laboratory, researching distortion effects in convoluted aeroengine intakes for combat aircraft.

Authors:

Rory Hine University of Cambridge
Dominic Cousins University of Cambridge
Leo Maden University of Cambridge
Samuel Walker University of Cambridge
Nick Atkins University of Cambridge
Samuel Grimshaw University of Cambridge
James Taylor University of Cambridge